At the same time the proportion of children cycling to school is now so low it is statistically too insignificant to be considered on its own, says Hume, of Deakin University's Centre for Physical Activity and Nutrition Research.

Hume says the decrease in what is known as active commuting has occurred at the same time as obesity rates among children have increased.

Although, the researcher says "it is drawing a long bow" to directly link the two, the decrease in walking and cycling to school is part of the overall reduction in physical activity amongst children.

"[Active commuting] makes an important contribution to children's overall physical activity," she says.

"Therefore, programs that aim to increase active commuting throughout childhood and in adolescence may have a positive effect on children's accumulated physical activity."

Study

Hume and colleagues took a closer look at the factors that impact on the amount of active transport among children and adolescents.

They tracked children and adolescents' mode of travel to school between 2004 and 2006.

During that period active commuting among the younger cohort, who were aged nine at the start of the study, increased significantly by 1.04 trips per week.

For the older adolescents (aged 14 at the start of the study) the increase was smaller with an additional in 0.65 trips per week.

Hume says interestingly there was no gender difference in the rates of walking to school.

"Although small, the observed increase in active commuting across the two years of the study might be attributable to age-related increases in independence and autonomy," Hume says.

Critical factors

For the younger cohort, Hume says the study highlighted one factor as critical to whether the children actively commuted.

"Children of parents who reported that the child had many friends in their area were twice as likely as to increase their active commuting compared with other children [in terms of mean trips per week]," she says.

Hume says this is related to the children having someone to walk with to school making the activity safer in parents' eyes.

For adolescents, whether they walked or cycled to school was related to urban design issues such as the presence of pedestrian crossings and traffic lights.

"These findings highlight the importance of the presence of pedestrian infrastructure within close proximity to schools," says Hume.

"Policies that create safer routes to school and thus address parents' perceptions of pedestrian safety may have an important impact on active-commuting patterns among youth."

Hume says changes to enable more children to walk and cycle to school will also have long-term benefits to the environment by reducing reliance on cars.